Most calls are blocking in nature, and will not return until the send has completed (or has thrown an exception).

RemoteEndpoint remote = session.getRemote();

// Blocking Send of a BINARY message to remote endpoint
ByteBuffer buf = ByteBuffer.wrap(new byte[] { 0x11, 0x22, 0x33, 0x44 });
try
{
    remote.sendBytes(buf);
}
catch (IOException e)
{
    e.printStackTrace(System.err);
}

How to send a simple Binary message using the RemoteEndpoint. This will block until the message is sent, possibly throwing an IOException if unable to send the message.

RemoteEndpoint remote = session.getRemote();

// Blocking Send of a TEXT message to remote endpoint
try
{
    remote.sendString("Hello World");
}
catch (IOException e)
{
    e.printStackTrace(System.err);
}

How to send a simple Text message using the RemoteEndpoint. This will block until the message is sent, possibly throwing an IOException if unable to send the message.

If you have a large message to send, and want to send it in pieces and parts, you can utilize the partial message sending methods of RemoteEndpoint. Just be sure you finish sending your message (isLast == true).

RemoteEndpoint remote = session.getRemote();

// Blocking Send of a BINARY message to remote endpoint
// Part 1
ByteBuffer buf1 = ByteBuffer.wrap(new byte[] { 0x11, 0x22 });
// Part 2 (last part)
ByteBuffer buf2 = ByteBuffer.wrap(new byte[] { 0x33, 0x44 });
try
{
    remote.sendPartialBytes(buf1,false);
    remote.sendPartialBytes(buf2,true); // isLast is true
}
catch (IOException e)
{
    e.printStackTrace(System.err);
}

How to send a Binary message in 2 parts, using the partial message support in RemoteEndpoint. This will block until each part of the message is sent, possibly throwing an IOException if unable to send the partial message.

RemoteEndpoint remote = session.getRemote();

// Blocking Send of a TEXT message to remote endpoint
String part1 = "Hello";
String part2 = " World";
try
{
    remote.sendPartialString(part1,false);
    remote.sendPartialString(part2,true); // last part
}
catch (IOException e)
{
    e.printStackTrace(System.err);
}

How to send a Text message in 2 parts, using the partial message support in RemoteEndpoint. This will block until each part of the message is sent, possibly throwing an IOException if unable to send the partial message.

You can also send Ping and Pong control frames using the RemoteEndpoint.

RemoteEndpoint remote = session.getRemote();

// Blocking Send of a PING to remote endpoint
String data = "You There?";
ByteBuffer payload = ByteBuffer.wrap(data.getBytes());
try
{
    remote.sendPing(payload);
}
catch (IOException e)
{
    e.printStackTrace(System.err);
}

How to send a Ping control frame, with a payload of "You There?" (arriving at Remote Endpoint as a byte array payload). This will block until the message is sent, possibly throwing an IOException if unable to send the ping frame.

RemoteEndpoint remote = session.getRemote();

// Blocking Send of a PONG to remote endpoint
String data = "Yup, I'm here";
ByteBuffer payload = ByteBuffer.wrap(data.getBytes());
try
{
    remote.sendPong(payload);
}
catch (IOException e)
{
    e.printStackTrace(System.err);
}

How to send a Pong control frame, with a payload of "Yup I'm here" (arriving at Remote Endpoint as a byte array payload). This will block until the message is sent, possibly throwing an IOException if unable to send the pong frame.

To be correct in your usage of Pong frames, you should return the same byte array data that you received in the Ping frame.

However there are also 2 Async send message methods available:

Both return a Future<Void> that can be used to test for success and failure of the message send using standard java.util.concurrent.Future behavior.

RemoteEndpoint remote = session.getRemote();

// Async Send of a BINARY message to remote endpoint
ByteBuffer buf = ByteBuffer.wrap(new byte[] { 0x11, 0x22, 0x33, 0x44 });
remote.sendBytesByFuture(buf);

How to send a simple Binary message using the RemoteEndpoint. The message will be enqueued for outgoing write, but you will not know if it succeeded or failed.

RemoteEndpoint remote = session.getRemote();

// Async Send of a BINARY message to remote endpoint
ByteBuffer buf = ByteBuffer.wrap(new byte[] { 0x11, 0x22, 0x33, 0x44 });
try
{
    Future<Void> fut = remote.sendBytesByFuture(buf);
    // wait for completion (forever)
    fut.get();
}
catch (ExecutionException | InterruptedException e)
{
    // Send failed
    e.printStackTrace();
}

How to send a simple Binary message using the RemoteEndpoint, tracking the Future<Void> to know if the send succeeded or failed.

RemoteEndpoint remote = session.getRemote();

// Async Send of a BINARY message to remote endpoint
ByteBuffer buf = ByteBuffer.wrap(new byte[] { 0x11, 0x22, 0x33, 0x44 });
Future<Void> fut = null;
try
{
    fut = remote.sendBytesByFuture(buf);
    // wait for completion (timeout)
    fut.get(2,TimeUnit.SECONDS);
}
catch (ExecutionException | InterruptedException e)
{
    // Send failed
    e.printStackTrace();
}
catch (TimeoutException e)
{
    // timeout
    e.printStackTrace();
    if (fut != null)
    {
        // cancel the message
        fut.cancel(true);
    }
}

How to send a simple Binary message using the RemoteEndpoint, tracking the Future<Void> and waiting only prescribed amount of time for the send to complete, cancelling the message if the timeout occurs.

RemoteEndpoint remote = session.getRemote();

// Async Send of a TEXT message to remote endpoint
remote.sendStringByFuture("Hello World");

How to send a simple Text message using the RemoteEndpoint. The message will be enqueued for outgoing write, but you will not know if it succeeded or failed.

RemoteEndpoint remote = session.getRemote();

// Async Send of a TEXT message to remote endpoint
try
{
    Future<Void> fut = remote.sendStringByFuture("Hello World");
    // wait for completion (forever)
    fut.get();
}
catch (ExecutionException | InterruptedException e)
{
    // Send failed
    e.printStackTrace();
}

How to send a simple Binary message using the RemoteEndpoint, tracking the Future<Void> to know if the send succeeded or failed.

RemoteEndpoint remote = session.getRemote();

// Async Send of a TEXT message to remote endpoint
Future<Void> fut = null;
try
{
    fut = remote.sendStringByFuture("Hello World");
    // wait for completion (timeout)
    fut.get(2,TimeUnit.SECONDS);
}
catch (ExecutionException | InterruptedException e)
{
    // Send failed
    e.printStackTrace();
}
catch (TimeoutException e)
{
    // timeout
    e.printStackTrace();
    if (fut != null)
    {
        // cancel the message
        fut.cancel(true);
    }
}

How to send a simple Binary message using the RemoteEndpoint, tracking the Future<Void> and waiting only prescribed amount of time for the send to complete, cancelling the message if the timeout occurs.